Photochromic polyurethane laminate

ABSTRACT

A photochromic polyurethane laminate wherein the photochromic polyurethane layer of the laminate has been crosslinked with an isocyanate-active prepolymer using a crosslinking agent. The crosslinking agent is formulated to have at least three functional groups that are reactive with functional groups of the polyurethane or of the isocyanate-active prepolymer. A method of making the photochromic polyurethane laminate includes steps of causing the crosslinking.

RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 15/838,037 filed Dec. 11, 2017 entitledPhotochromic Polyurethane Laminate, which is a continuation of andclaims priority to U.S. patent application Ser. No. 14/864,748 filedSep. 24, 2015 entitled Photochromic Polyurethane Laminate (now U.S. Pat.No. 9,869,801 issued Jan. 16, 2018), which is a divisional of and claimspriority to U.S. patent application Ser. No. 13/563,236 filed Jul. 31,2012 entitled Photochromic Polyurethane Laminate (now U.S. Pat. No.9,163,108), which is a continuation-in-part of U.S. patent applicationSer. No. 12/763,103 filed Apr. 19, 2010 entitled PhotochromicPolyurethane Laminate; and claims priority to U.S. ProvisionalApplication Ser. No. 61/170,473 filed Apr. 17, 2009 entitledPhotochromic Polyurethane Laminate With Improved Adhesion And Strength;all of which are hereby incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates generally to a photochromic laminate thatcan be applied to polymeric surfaces or can be used by itself as aphotochromic element. The present invention also relates to aphotochromic laminate that is capable of withstanding high temperaturesand can be incorporated into plastic lenses by means of injectionmolding or casting. The present invention further relates to aphotochromic laminate that is excellent in both control of thickness andsurface smoothness of the photochromic layer, and thereof exhibitsuniform darkness at the activated state.

DESCRIPTION OF THE RELATED ART

Photochromic articles, particularly photochromic plastic materials foroptical applications, have been the subject of considerable attention.In particular, photochromic ophthalmic organic glass lenses (e.g.,injection molded polycarbonate lenses or CR39 cast lenses) have beencommercially desirable because of the weight advantage and impactresistance they offer over glass lenses. Moreover, photochromictransparencies, e.g., photochromic window panes for vehicles such ascars, boats and airplanes, have been of interest because of thepotential safety features that such transparencies offer.

The use of polycarbonate ophthalmic lenses, particularly in the UnitedStates, is widespread. The demand for sunglasses that are impactresistant has increased as a result of extensive outdoor activity.Materials such as polycarbonate, however, have not historically beenconsidered optimal ophthalmic sunglass lenses with photochromic dyes dueto slow activation rates, slow fading (bleaching) rate, and lowactivation intensity.

Nonetheless, there are several existing methods to incorporatephotochromic properties into lenses made from materials such aspolycarbonate. One method involves applying to the surface of a lens acoating containing dissolved photochromic compounds. For example,Japanese Patent Application 3-269507 discloses applying a thermosetpolyurethane coating containing dissolved photochromic compounds on thesurface of a lens. U.S. Pat. No. 6,150,430 similarly discloses aphotochromic polyurethane coating for lenses. The content of each ofthese prior art references is incorporated by reference.

Another method involves coating a lens with an imbibing process. Aprocess described in U.K. Pat. No. 2,174,711 or U.S. Pat. No. 4,968,454,both of which are incorporated by reference herein, is used to imbibe asolution containing photochromic compounds into the base coatingmaterial. The most commonly used base material is polyurethane.

The two methods described above, however, which involve coating orimbibing the lens after it is molded, have significant shortcomings. Forexample, typically a coating of about 25 μm or more is needed in orderfor a sufficient quantity of photochromic compounds to becomeincorporated into the base of the lens and thereby provide the desiredlight blocking quality when the compounds are activated. This relativelythick coating is not suited for application on the surface of asegmented, multi-focal lens because an unacceptable segment line andcoating thickness nonuniformity around the segment line are produced.The desired surface smoothness is also affected.

Turning to lenses made from injection molded techniques, lenses made ofplastic materials such as polycarbonate can be produced by an injectionmolding process that uses an insert placed in the mold prior to theinjection of the molten plastic material (insert-injection molding). Theinsert can be the means by which photochromic properties areincorporated into the lenses. Insert injection molding is a processwhereby the molten plastic resin is injection molded onto an inserthaving, e.g., a photochromic property, that has been placed in the moldcavity. An example of this process is disclosed in commonly assignedU.S. Pat. No. 6,328,446 (which is hereby incorporated by reference inits entirety), whereby a photochromic laminate is first placed inside amold cavity. Molten polycarbonate lens material is next injected intothe cavity and fused to the back of the photochromic laminate. Thisproduces a photochromic polycarbonate lens. Because the photochromicfunction is provided by a thin photochromic layer in the laminate, it ispossible to then finish-grind the photochromic polycarbonate lenses withany kind of surface curvature without damaging or degrading thephotochromic properties of the lens.

Photochromic lenses can also be made by the cast process as described inUS Patent Publication 2007/0122626, the entire contents of which isincorporated by reference. The cast molding process includes placing thephotochromic film in a cast mold, then introducing the cast monomer intothe mold and then curing the monomer in the mold into lenses either byheat or by radiation.

Resin laminates with photochromic properties that could be consideredfor use in the above-mentioned insert-injection molding technique or thecast molding process have been disclosed in many patents andpublications. Examples include Japanese Patent Applications 61-276882,63-178193, 4-358145, and 9-001716; U.S. Pat. No. 4,889,413; U.S. PatentPublication No. 2002-0197484; and WO 02/093235 (each of which isincorporated by reference herein). The most commonly used structure is aphotochromic polyurethane host layer bonded between two transparentresin sheets. Although the use of polyurethane as a photochromic hostmaterial is well known, photochromic polyurethane laminates designedespecially for making photochromic polycarbonate lenses through, forexample, the insert-injection molding method are unique.

Problems associated with conventional insert injection moldingtechniques in the manufacture of photochromic lens using prior artphotochromic polyurethane laminates include polyurethane bleeding andpoor replication of lens segment lines. “Bleeding” occurs from thedeformation of the polyurethane layer during injection moldingprocessing. In particular, bleeding occurs when the polyurethane layermelts and escapes from its position between the two transparent sheetsof the laminate during the high temperature and high-pressure injectionmolding process. The inventors are of the view that bleeding mostfrequently results from an excess amount of polyurethane and from usingtoo soft a polyurethane material. The inventors are also of the viewthat poor replication of segment lines occurs when the layer ofpolyurethane is too thick and movement of the laminate occurs aspressure from the mold is applied.

In attempts to address at least the bleeding problem, it is preferred tohave the polyurethane cross-linked thus making a harder and hightemperature resistant polyurethane material. However, cross-linkedpolyurethane, once made, is difficult to laminate between transparentresin sheets and arrive at a suitable photochromic laminate. Forexample, a cross-linked polyurethane, once made, is not soluble in asolvent and thus cannot be laminated between transparent resin sheetsusing the casting method. A cross-linked polyurethane also neither meltsnor softens at temperature ranges necessary for making a laminate withtransparent resin sheets through the extrusion process. One method thathas been considered for incorporating cross-linked polyurethane into alaminate is to start with a liquid polyurethane system such as the onedescribed in U.S. Patent Publication No. 2002-0197484 (incorporated byreference). To make the laminate efficiently, a web coat-laminate linesuch as the one described in Japan Patent Laid Open 2002-196103(incorporated by reference), might be used. The coating equipment iscapable of coating a uniform layer of liquid polyurethane mixture.

However, this layer will only be partially solidified (or cured) at themoment of in-line lamination. Consequently, any surface defects in theresin sheet and/or the lamination rollers are easily transferred to thesoft polyurethane layer during lamination. The most often seen defectsin the polyurethane layer include thickness un-evenness across the weband thin spots due to uneven pressure at lamination or improperhandling. In order to have the polyurethane layer firm enough towithstand the necessary pressure during lamination and avoid thesedefects, it needs to first be cured for a certain amount of time.Curing, however, slows down the processing or renders the webcoating-laminating approach impossible.

SUMMARY OF THE INVENTION

In view of the above, a need exists to overcome the problems andshortcomings associated with existing polyurethane laminates havingphotochromic properties and methods of making such laminates.

The concepts disclosed in U.S. Patent Publication No. 2005/0233153 (the“′153 Publication”), the entire contents of which are incorporatedherein, attempt to address at least some of these needs. However, theneed exists to further overcome these problems and shortcomings evenbeyond the teachings of the '153 Publication.

For example, the present application discloses the concept ofintroducing a network structure into the molecular make up of aphotochromic polyurethane layer by adding a crosslinking agent havingthree or more functional groups into the formulation. Said functionalgroups are preferably either active hydroxyl groups or NCO groups. Thiscreates a network structure by the occurrence of a crosslinking reactionduring the curing stage of the polyurethane thereby improving theproperties of the layer.

Some of the resulting improved properties over at least the teachings ofthe '153 Publication include increased mechanical strength, improvedchemical resistance, improved adhesion of the polyurethane layer to thefirst and second transparent resin sheet; improved cohesion withinphotochromic polyurethane layer; improved heat resistance of thelaminate, improved humidity resistance of the laminate, and improvedbleeding resistance of the laminate during the molding process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table setting forth the formulation of various specificembodiments of a laminate in accordance with the present inventiveconcepts;

FIG. 2 is a table setting forth physical properties of the variousspecific embodiments of FIG. 1;

FIG. 3 is a table setting forth representative embodiments ofcrosslinking agents used in the various specific embodiments of FIG. 1.

FIG. 4 is a table setting forth the formulation of various specificembodiments of a laminate in accordance with the present inventiveconcepts.

FIG. 5 is a table setting forth physical properties of the variousspecific embodiments of FIG. 4.

FIG. 6 is a schematic description of a room temperature testconfiguration for measuring peel strength of embodiments of the presentinvention.

FIG. 7 is a schematic description of a high temperature testconfiguration for measuring peel strength of embodiments of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment of the present invention includes a photochromicpolyurethane laminate that includes a first resin layer, a second resinlayer and a polyurethane layer having photochromic properties interposedbetween the first and second resin layer. The polyurethane layer isformulated from a polyurethane that has been crosslinked with anisoycanate-active prepolymer via a crosslinking agent. In a preferredembodiment, the crosslinking agent has molecules that have at leastthree functional groups that are reactive with either a functional groupof the polyurethane or a functional group of the isocyanate-activeprepolymer. In other words, the at least three functional groups arereactive with a functional group of at least one of the polyurethane andisocyanate-active prepolymers. A crosslinked photochromic polyurethanelaminate of this type leads to a laminate that has improved mechanicaland material properties thus providing a laminate that is more versatileand robust for use in manufacturing photochromic articles such asinjection molded photochromic lenses and/or cast photochromic lenses.

In one preferred embodiment the crosslinking agent is a multifunctionalalcohol where at least three functional groups react with the isocyanategroups of the isocyanate prepolymer. In another preferred embodiment,the crosslinking agent is a multifunctional isocyanate, isocyanateoligomers or isocyanate prepolymers where the functional groups reactwith the hydroxyl groups of the polyurethane.

Another aspect of the present invention is the method of making aphotochromic polyurethane laminate. In one preferred embodiment, theprocess includes providing a polyurethane, dissolving the polyurethaneinto a solution; adding an isocyanate prepolymer into the solution,introducing a crosslinking agent into the solution, wherein thecrosslinking solution has at least three functional groups. At least onephotochromic dye is then introduced into the solution. The functionalgroups of the crosslinking agent react with a functional group of atleast one of the polyurethane and isocyanate prepolymer so as to form acrosslinked photochromic polyurethane layer. This layer is thensandwiched between a first and second resin sheet.

Specific preferred embodiments of the aforementioned inventive conceptsare discussed below.

Synthesis Example 1: Synthesis of Thermoplastic Polyurethane

Step 1: Synthesis of isocyanate prepolymer.

In a 3-necked flask equipped with an overhead stirrer, thermocouple, anda vacuum adapter, 1226.0 g (9.27 equivalents) of4,4′-dicyclohexylmethanediisocyanate (H12MDI, available from Bayer asDesmodur W) was charged into the reactor and stirred at ambienttemperature. 2,000 g (4.02 equivalents) of a polycaprolactone diolhaving an OH number of 112 mg KOH/g and a number average molecularweight of about 1,000 g/mole (available from Dow Chemical as Tone™ 2221)was preheated in an oven to 80° C. and added to the reactor. The mixturewas allowed to stir for about 15 minutes, before adding 16 g ofdibutyltin dilaurate catalyst (available from Air Products as T-12). Thereaction flask was evacuated (<0.1 mm HG) and held at 90° C. for 6hours. An aliquot of the prepolymer was withdrawn and titrated forisocyanate content using standard n-butyl amine titration. Theisocyanate content was found to be 6.75% (theory; 6.83%). The molecularweight is in the range of 5,000-15,000

Step 2: Synthesis of thermoplastic polyurethane

A thermoplastic polyurethane having a theoretical NCO index of 95 wasprepared as follows. The isocyanate prepolymer (1854.4 g) prepared instep 1 was heated in vacuum oven (<0.1 mm HG) with stirring to 80° C.and 1,4-butane-diol (145.6 g) as the chain extender and 6 g ofdibutyltin dilaurate catalyst were combined with the prepolymer whilestirring. The mixture was stirred for 30 seconds and subsequently pouredinto a Teflon lined tray. The tray containing the casting was cured inan oven at 85° C. for 24 hours. The thermoplastic polyurethane obtainedhad a molecular weight of 100,000 measured by Viscotek GPC.

Synthesis Example 2: Synthesis of Isocyanate-Active Prepolymer

In a 3-necked flask equipped with an overhead stirrer, thermocouple, anda vacuum adapter, 1210 g (9.15 equivalents) of4,4′-dicyclohexylmethanediisocyanate (H12MDI, available from Bayer asDesmodur W) was charged into the reactor and stirred at ambienttemperature. 3000 g (6.03 equivalents) of a polycaprolactone diol havingan OH number of 112 mg KOH/g and a number average molecular weight ofabout 1,000 g/mole (available from Dow Chemical as Tone™ 2221) waspreheated in an oven to 80° C. and added to the reactor. The mixture wasallowed to stir for about 15 minutes, before adding 12 g of dibutyltindilaurate catalyst (available from Air Products as T-12). The reactionflask was evacuated (<0.1 mm HG) and held at 90° C. for 6 hours. Analiquot of the prepolymer was withdrawn and titrated for isocyanatecontent using standard n-butyl amine titration. The isocyanate contentwas found to be 3.07% (theory; 3.10%). The polyurethane prepolymer had amolecular weight of 6,000 measured by Viscotek GPC.

Synthesis Example 3: Synthesis of Thermoplastic Polyurethane

595.5 g of isocyanate prepolymer prepared in step 1 of synthesis example1 was heated in vacuum (<0.1 mm HG) with stirring to 80° C. and combinedwith 48.0 g of 1,4-butane-diol while stirring. The mixture was stirredfor 30 seconds and subsequently poured into a Teflon lined tray. Thetray containing the casting was cured in an oven at 85° C. for 24 hours.The thermoplastic polyurethane obtained had weight average molecularweight of 75,230 measured by GPC.

Synthesis Example 4: Synthesis of Isocyanate-Active Prepolymer

In a 3-necked flask equipped with an overhead stirrer, thermocouple, anda vacuum adapter, 335 g (2.55 equivalents) of4,4′-dicyclohexylmethanediisocyanate (available from Bayer as DesmodurW) was charged into the reactor and stirred at ambient temperature.664.8 g (1.33 equivalents) of a polycaprolactone diol having an OHnumber of 112 mg KOH/g (available from Dow Chemical as Tone™ 2221) waspreheated in an oven to 80° C. and added to the reactor. The mixture wasallowed to stir for about 15 minutes, before adding 2.5 g of dibutyltindilaurate catalyst (available from Air Products as T-12). The reactionflask was evacuated (<0.1 mm HG) and held at 80° C. for 3 hours andcooled down. The resulted product was titrated and resulted in NCOcontent of 5.10%.

MAKING LAMINATES Examples 1 to 14

A quantity of the thermoplastic polyurethane (TPU) prepared in SynthesisExample 1 was weighed and is identified as row 1 in FIG. 1. A solutioncontaining about 23% solute and 77% THF solution is prepared bydissolving the thermoplastic polyurethane in THF at room temperature. Tothe solution was further added the quantity of the isocyanate prepolymerprepared in Synthesis Example 2 identified in row 2 of FIG. 1, andcrosslinking agent identified in row 3 of FIG. 1 in the quantity asshown in row 4 of FIG. 1. Further details of the crosslinking agent areidentified in the table of FIG. 3. Into the mixture were also added thequantity of photochromic dye and additives as shown in rows 5 to 8 ofFIG. 1. The mixture was stirred at room temperature for 3 hours and thenwas cast on an easy release liner (available from CPFilms as T-50) witha draw bar targeting a 38 micrometer dry film thickness. The solvent inthe cast film was evaporated at 60° C. for 5 minutes using airflow abovethe film. The dried film was transfer-laminated between two resin sheetsidentified in row 9 of FIG. 1 with a bench top roller laminator. After 4days under ambient temperature (about 70° F.) the laminate was cured at60° C. for 4 days.

It will be noted that Example No. 11 in FIG. 1 is designated as the“comparative” example. This is because Example 11 reflects aphotochromic polyurethane laminate where the polyurethane layer is notcrosslinked. As such, Example 11 provides a comparison of the materialproperties resulting from the present invention and the improvementstherein.

Examples 15-20

A quantity of the thermoplastic polyurethane (TPU) prepared in SynthesisExample 1 or Synthesis Example 3 was weighed as shown in row (1) and row(2), respectively, in FIG. 4. A 27% of THF solution is prepared bydissolving the thermoplastic polyurethane in THF at room temperature. Tothe solution was further added the quantity of the isocyanate prepolymerprepared in Synthesis Example 2 or Synthesis Example 4 as shown in row(3) and row (4), respectively, in FIG. 4. Quantities of 2% Di-TMPsolution in THF was added as shown in row (6) in FIG. 4. Into themixture were also added the quantities of photochromic dye and additivesas shown in rows (7) to (10) in FIG. 4. The mixture was stirred at roomtemperature for 3 hours before cast on an easy release liner (availablefrom CPFilms as T-50) with draw bar targeting a dry film thickness as inrow (11) in FIG. 4. The solvent in the cast film was evaporated at 60°C. for 5 minutes with airflow above the film. The dried film wastransfer-laminated between two polycarbonate sheets with a bench toproller laminator. After 4 days under ambient, the laminate was cured at70° C. for 4 days.

Various tests of the examples were then tested for various properties.The tests used to determine those properties are discussed below. Theresults of those tests are set forth in the table of FIGS. 2 and 5.

Test procedures used in obtaining the material property results setforth in the table of FIGS. 2 and 5 are set forth below:

1. Room Temperature T-Peel Strength: 1 cm×7 cm strips of the laminateare punched out of the cast sheet with a hand punching press. T-Peelstrength, i.e., the adhesion strength of the laminate was measured onthe samples on Instron at speed of 6 in/min at room temperature. Inparticular, for each strip, the edges of the resin sheet on either sideof the photochromic polyurethane layer are pulled away from each otherat room temperature at a pre-set rate (e.g., 6 in/min). The resultingmeasured value is the force per width of the laminate required toseparate the two resin sheets at room temperature. A schematic drawingof the Room Temperature T-Peel Separation test is depicted in FIG. 6.

2. High Temperature T-Peel Separation: 1 cm×7 cm strips of the laminateare punched out of the cast sheet with the hand punching press. The ovenwas set at 130° C. The sample was then hung in an oven, one edge of thetop resin sheet of a strip attached to the oven hood and thecorresponding edge of the bottom resin sheet of the strip attached to230 g weight for 10 minutes. The distance separating the top and bottomresin sheets was measured at the end of 10 minutes. If the two resinsheets were separated completely before 10 minutes, then the time to thedrop of the weight was recorded. Separation length was then extrapolatedfor the total 10 minutes of the test. A schematic drawing of the HighTemperature T-Peel Separation test is depicted in FIG. 7.

3. Solvent resistance: 3 strips of 1 cm×7 cm of the laminate were placedin an oven at 235° F. for 5 minutes. The laminate was then peeled apartsuch that one of the resin sheets is separated from the other resinsheet and the crosslinked photochromic polyurethane is left deposited onone or both of the resin sheets. The strips were then placed in aTechSpray AK225 solvent for 1 to 2 minutes. The polyurethane was thenscraped off each laminate side. The collected polyurethane was thendried in a vacuum oven overnight at 60° C. The dried polyurethane wasplaced in a 20 ml glass vial with 10 ml THF. The behavior of the polymerwas then observed after 3 hours at room temperature to see to whatextent the polyurethane was dissolved.

4. Bleeding resistance: The cast sheet of laminate was punched into 86mm diameter disks. Each disk was placed in a molding cavity.Polycarbonate resin was injected behind the disk to performinsert-injection molding as discussed above. The edge of the disk wasthen checked for any bleeding of the photochromic layer outside of thedisk. In this regard, it is noted from FIG. 1 that Examples 13 and 14 donot contain bleeding resistance data. This is because the transparentresin sheets for Examples 13 and 14 were composed PMMA and CelluloseTriacetate, respectively. These types of materials are more suited forthe manufacture of cast photochromic lenses and not injection moldedphotochromic lenses. Hence, the bleeding test was not performed forExamples 13 and 14.

Crosslinking Agents

The characteristics of crosslinking agents used in connection with thepresent invention are described below.

Molecules of suitable crosslinking agents for the present inventioncontain more than 2 functional groups that react with either thehydroxyl group in the thermoplastic polyurethane or the isocyanate groupin the isocyanate prepolymer. Preferred embodiments of such crosslinkingagents are discussed below.

One preferred embodiment of a crosslinking agent is multifunctionalalcohols having not less than 3 alcohol functional groups. The alcoholfunctional groups react with isocyanate group in the isocyanateprepolymer to form the urethane linkage and hence the three-dimensionalpolymer molecule structure. Preferred embodiments include, but are notlimited to, trimethylolpropane, trimethylolethane, glycerin,pentaerythritol and di(trimethylolpropane).

Another preferred embodiment is an oligomer with more than two OHfunctional groups that can react with the isocyanate group in theisocyanate prepolymer. A preferred embodiment includes, but is notlimited to, trimethylolpropane propoxylate with average molecule Mw=308as supplied by Sigma Aldrich.

Another preferred embodiment is a solution that has molecules with totalamino and OH groups not less than two wherein these groups react withisocyanate group of the prepolymer. Preferred embodiments include, butare not limited to, N,N-Bis(2-hydroxyethyl)isopropanolamine,N,N,N′,N′-Tetrakis(2-Hydroxypropyl)-ethylenediamine.

Another preferred embodiment includes multifunctional isocyanates,isocyanate oligomers and isocyanate prepolymers, each having at least 3NCO groups that react with the hydroxyl group of the polyurethane.Preferred embodiments include, but are not limited to, Desmodur N75BA,Desmodur RFE, Desmodur RE supplied by Bayer Materials and Irodur E310supplied by Huntsman. In this regard, the crosslinking agent used inExample 12 of FIG. 1 was a multifunctional isocyanate.

Another preferred embodiment includes blocked isocyanates with not lessthan 3 isocyanate functional groups, those groups reacting with thehydroxyl group of the polyurethane. When unblocked, mostly by elevatedtemperature, the isocyanate groups react with the hydroxyl group of thepolyurethane. Crosslinking agents with blocked isocyanates can beproduced by reacting the multifunctional isocyanates with differentblocking agents. Each blocking agent has a different de-blockingtemperature, the temperature at which the dissociation reaction occursthat separates the blocking agent from the blocked isocyanate andprovide the isocyanate functional group available for reaction. Examplesof blocking agents are the oxime agent such as 3,5-dimethyl pyrazol,2,6-dimethyl-4-heptanone oxime, methyl ethyl ketoxime, 2-heptanoneoxime; 1,24-triazole; ϵ-caprolactam; and the alcohols such asnonylphenol, t-butanol, propylene glycol, isopropanol, methanol,n-butanol, n-propanol, n-hexanol, n-pentanol.

Examples of crosslinking agents with blocked isocyanate groups includethe polyether aromatic based polyurethane prepolymer Impranil productline supplied by Bayer Coating such as Impranil HS-62, Impranil HS-130or the commercially available Duranate 17B-60PX, Duranate TPA-880X,Duranate E402-B80T, Duranate MF-B60X manufactured by Asahi KaseiChemicals Corporation.

Another preferred embodiment includes heat-activated urea compounds withnot less than two urea functional groups, wherein the urea functionalgroups react with the hydroxyl groups of the polyurethane at hightemperature through allophanate and biuret formation. Preferredembodiments of such heat-activated ureas include, but are not limitedto, 3,3′-hexamethylenebis(1,1′-dipropylurea) and3,3′-(4-methyl-1,3-phenylene)bis(1,1′-dipropylurea).

Another preferred embodiment includes (hydroxyalkyl)urea compounds withsingle urea group and 2 hydroxyl groups, where the groups react with theisoycanate group of the prepolymer. Preferred embodiments include, butare not limited to, N,N-bis(2-hydroxyethyl)urea,tetrakis(2-hydroxylethyl)urea, tris(2-hydroxyethyl)urea,N,N′-bis(2-hydroxyethyl)urea, N,N′-bis(3-hydroxyethyl)urea,N,N′-bis(4-hydroxybutyl)urea and 2-urea-2-ethyl-1,3-propanediol.

Transparent Resin Sheet

There are many materials that can be used to make transparent resinsheets so long as such a resin has a high transparency. When thephotochromic polyurethane laminate of the present invention is used in athermoplastic article such as a spectacle lens, the transparent resinsheets of the laminate are preferably comprised of a resin material thatis thermally fusible to the article base material so that thephotochromic laminate is tightly integrated with the article base whenproduced with the injection molding process. Thus, it is more preferredto have the same kind of material in both the article base and thetransparent resin sheets.

Suitable sheet resin materials include polycarbonate, polysulfone,cellulose acetate buturate (CAB), polyacrylate, polyester, polystyrene,copolymer of acrylate and styrene.

A polycarbonate-base resin is particularly preferred because of its hightransparency, high tenacity, high thermal resistance, high refractiveindex, and most importantly its compatibility with the article basematerial when polycarbonate photochromic lenses are produced with thephotochromic polyurethane laminate of the present invention by theinjection molding process.

A typical polycarbonate based resin is polybisphenol-A carbonate. Inaddition, examples of polycarbonate based resin includehomopolycarbonate such as 1,1′-dihroxydiphenyl-phenylmethylmethane,1,1′-dihroxydiphenyl-diphenylmethane, 1,1′-dihydroxy-3,3′-dimethyldiphenyl-2,2-propane, their mutual copolymer polycarbonate and copolymerpolycarbonate with bisphenol-A.

One preferred embodiment of the transparent resin sheet for use inmaking a cast photochromic lens is Celluloase Acylate film because ofits high transparency, high thermal resistance, and more important, itssimilar refractive index and its compatibility to CR39 resin when a CR39photochromic lenses are produce with the photochromic polyurethanelaminate of the present invention by the casting process.

Cellulose Acylate film (all or part of the hydroxyl groups at 2-, 3- and6-positions of cellulose molecules are esterified with an acyl group).Acetyl group is a preferable substitution of the hydroxyl groups. Also,an acyl group with two or more carbon atoms, substituting the hydroxylgroup of cellulose may be an aliphatic group or an aryl group. Examplescan be an alkylcarbonyl ester, and alkenylcarbonyl ester, an aromaticcarbonyl ester or an aromatic alkylcarbonyl ester of cellulose.

Examples of cellulose acylate resin sheets are cellulose diacetate,cellulose triacetate.

The foregoing embodiments are provided by way of example only. The scopeof the invention is to be defined only by the scope of the followingclaims.

What is claimed is:
 1. A photochromic polyurethane laminate comprising:a crosslinked photochromic polyurethane layer prepared from acomposition comprising: a polyurethane; an isocyanate prepolymer; acrosslinking agent comprising a (hydroxyalkyl)urea compound having onefunctional urea group and two functional hydroxyl groups; and aphotochromic agent; a first resin layer attached to a first side of thecrosslinked photochromic polyurethane layer; and a second resin layerattached to a second side of the crosslinked photochromic polyurethanelayer.
 2. The photochromic polyurethane laminate according to claim 1,wherein the polyurethane is formed from a polycaprolactone diol.
 3. Aphotochromic polyurethane laminate comprising: a first resin layer; asecond resin layer; and a crosslinked photochromic polyurethane layerdisposed between the first and the second resin layers, the crosslinkedphotochromic polyurethane layer formed of a composition comprising: apolyurethane; an isocyanate prepolymer; a crosslinking agent having atleast three functional groups that react with hydroxyl groups of thepolyurethane and isocyanate groups of the isocyanate prepolymer; and atleast one photochromic compound.
 4. The photochromic polyurethanelaminate according to claim 3, wherein the crosslinking agent havingsaid at least three functional groups is a (hydroxyalkyl)urea compoundcomprising one functional urea group and at least two functionalhydroxyl groups.
 5. The photochromic polyurethane laminate according toclaim 4, wherein said one functional urea group of said(hydroxyalkyl)urea compound reacts with said hydroxyl groups of thepolyurethane.
 6. The photochromic polyurethane laminate according toclaim 4, wherein said at least two functional hydroxyl groups of said(hydroxyalkyl)urea compound reacts with said isocyanate groups of theisocyanate prepolymer.